Supercritical fluid extraction is becoming a widely used method for the extraction of organic compounds from solid matrices. This extraction is used to prepare sample extracts for subsequent chemical analysis. Laboratory versions of supercritical fluid extraction devices are commercially available, for example from Suprex Corporation, Pittsburgh, Pa. However, laboratory versions of SFE apparatus are not practical for use in the field because of size and weight considerations. In addition, many commercial units require utilities (e.g., compressed air, cryogenic cooling fluids) that are impractical for use in the field.
The general problem of obtaining samples from the field using supercritical fluid extraction has been addressed. Specifically, U.S. Pat. No. 5,087,360 issued Feb. 11, 1992 to Wright et al. shows a field portable supercritical fluid extraction apparatus. This apparatus requires storing solvent gas (carbon dioxide). A high pressure liquid chromatography pump is used to raise the pressure to between 300 to 400 bar. A cooling system is included to cool the pump to avoid vapor lock. For carbon dioxide, cooling was between 0.degree. and 9.degree. C. The apparatus weight was about 25 kilograms and the weight of the solvent vessel and solvent was about 25 kilograms for a total system weight of about 50 kilograms.
It is desirable to further reduce weight and complexity of the apparatus for extracting samples in the field.